Add S3 backend and storage verification

tests/unit/test_dataplane_inproc.py

@@ -158,6 +158,24 @@ async def test_ingest_hints_override_primary_algorithm(
     assert result.primary_digest.hex == result.sha256_digest.hex
 
 
+async def test_ingest_hints_route_to_named_backend(tmp_path: Path) -> None:
+    local = LocalBackend(tmp_path / "local", backend_id="local")
+    archive = LocalBackend(tmp_path / "archive", backend_id="archive")
+    dp = InProcessDataPlane(
+        {"local": local, "archive": archive},
+        default_backend_id="local",
+    )
+
+    result = await dp.ingest_stream(
+        _stream(b"route-me"),
+        hints=IngestHints(backend_id="archive"),
+    )
+
+    assert result.receipt.backend_id == "archive"
+    assert not (local.root / result.receipt.object_key).exists()
+    assert (archive.root / result.receipt.object_key).exists()
+
+
 async def test_serve_missing_object_propagates_object_not_found(
     dataplane: InProcessDataPlane,
 ) -> None: